Display device

ABSTRACT

According to one embodiment, a display device comprises a flexible substrate, a first insulating film disposed on the flexible substrate, a switching element disposed on the first insulating film, a signal wiring electrically connected with the switching element, a first organic film disposed on the signal wiring, a connection wiring disposed on the first organic film, a second organic film disposed on the connection wiring and a pad electrode disposed on the second organic film. The connection wiring is located between the first organic film and the second organic film and is in contact with the first organic film and the second organic film.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.16/788,830 filed Feb. 12, 2020, which is a continuation of U.S.application Ser. No. 16/504,943 filed Jul. 8, 2019, which is acontinuation of U.S. application Ser. No. 15/478,400 filed Apr. 4, 2017,and is based upon and claims the benefit of priority from JapanesePatent Application No. 2016-075331, filed Apr. 4, 2016, the entirecontents of each of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a display device.

BACKGROUND

Flat-panel display devices such as those having liquid crystal panels ororganic electroluminescent (EL) panels have been used in various fields.Recently, flexible display devices capable of being bent have beendeveloped by using flexible substrates formed of flexible materials asboards for display devices.

In general, a display device includes a display area where an image isdisplayed, and a frame area located around the display region andconnected to drive circuits and external circuits.

This display device is strongly required to make a frame area narrower(i.e., to narrow a frame) to further increase the display area from theviewpoint of performance, design, and the like. To narrow the frame ofthe flexible display device, the frame area of the flexible displaydevice is bent, and the frame area outside the bent area is arranged ona back surface side of the flexible display device, thereby effectivelyenlarging the display area.

In the prior art display device, an inorganic electrically insulatingfilm is sometimes disposed on the entire surface of the flexiblesubstrate in order to prevent moisture from entering therein. Theinorganic insulating film generally has a higher resistance to bendingstress as compared to the flexible substrate. Therefore, in the casewhere the inorganic insulating film is present on the area to be bent inthe display device, bending stress is applied to the inorganicinsulating film when the display device is bent, which may lead tocracking of the inorganic insulating film. With the cracking of theinorganic insulating film, the wiring disposed on the inorganicinsulating film may be broken.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic plan view of a display device according to a firstembodiment.

FIG. 2 is a schematic cross-sectional view taken along line II-IT inFIG. 1.

FIG. 3 is a schematic cross-sectional view taken along line III-III inFIG. 1.

FIG. 4 is an enlarged plan view of a terminal area in the display deviceof the first embodiment.

FIG. 5A is a schematic side view illustrating a pre-bent state of thedisplay device of the first embodiment.

FIG. 5B is a schematic side view illustrating a bent state of thedisplay device of the first embodiment.

FIG. 6 is a schematic cross-sectional view of a display device accordingto a second embodiment, corresponding to the cross-sectional view ofFIG. 2.

FIG. 7 is a schematic cross-sectional view of a display device accordingto the second embodiment, corresponding to the cross-sectional view ofFIG. 3.

DETAILED DESCRIPTION

In general, according to one embodiment, a display device comprises aflexible substrate, a first insulating film disposed on the flexiblesubstrate, a switching element disposed on the first insulating film, asignal wiring electrically connected with the switching element, a firstorganic film disposed on the signal wiring, a connection wiring disposedon the first organic film, a second organic film disposed on theconnection wiring and a pad electrode disposed on the second organicfilm. The connection wiring is located between the first organic filmand the second organic film and is in contact with the first organicfilm and the second organic film.

Embodiments will be described hereinafter with reference to theaccompanying drawings. Structures common in embodiments are denoted bythe same reference numbers or symbols, duplicate explanations beingomitted. Each figure is an exemplary diagram of an embodiment to aidunderstanding of the embodiment. The shapes, dimensions or ratios in thedrawings may differ from those of the actual device, but they are merelyexemplary and in no way restrict the interpretation of the invention.

An organic electroluminescent (EL) display device will be explained asan example of a display device in the following embodiments, but theinvention can also be applied to the other display devices such as aliquid crystal display device. In addition, a top-emission type organicEL display device will be explained in the following embodiments, butthe invention can also be applied to a bottom-emission type organic ELdisplay device.

First Embodiment

A display device DSP-1 of the first embodiment will be described withreference to FIG. 1 to FIG. 5B. FIG. 1 is a schematic plan view of thedisplay device DSP-1. FIG. 2 is a schematic cross-sectional view takenalong line II-II in FIG. 1. FIG. 3 is a schematic cross-sectional viewtaken along line III-III in FIG. 1. FIG. 4 is an enlarged plan view of aterminal area in the display device DSP-1. FIG. 5A is a schematic sideview illustrating a pre-bent state of the display device DSP-1. FIG. 5Bis a schematic side view illustrating a bent state of the display deviceDSP-1.

In the embodiment described herein, a direction parallel to short sidesof the display device is referred to as a first direction X, a directionparallel to long sides of the display device DSP is referred to as asecond direction Y, and a direction perpendicular to the first directionX and the second direction Y is referred to as a third direction Z. Thefirst direction X and the second direction Y are orthogonal to eachother but may intersect at an angle other than 90 degrees.

In addition, a positive orientation of the third direction Z is definedas an upper or upward orientation while a negative orientation of thethird direction Z is defined as a lower or downward orientation, in theembodiments. According to “a second member above a first member” and “asecond member below a first member”, the second member may be in contactwith the first member or may be distant from the first member. In thelatter case, a third member may be interposed between the first memberand the second member. In contrast, according to “a second member on afirst member” and “a second member under a first member”, the secondmember is in contact with the first member.

Seeing a flexible substrate SUB from the positive orientation of thethird direction Z is defined as planar view in the present embodiment.

As shown in FIG. 1, the display device DSP-1 includes an image displayarea DA disposed on the flexible substrate SUB and a frame-shapednon-display area FA surrounding the image display area DA. Thenon-display area FA includes a terminal area TA located on, for example,the right side of the image display area DA so as to be adjacent to theimage display area DA. The terminal area TA includes a contact area CAadjacent to the image display area DA, a bend area BA adjacent to thecontact area CA, and a pad area PA adjacent to the bend area BA. In thepresent embodiment, the contact area CA corresponds to a first area, thebend area BA corresponds to a second area, and the pad area PAcorresponds to a third area.

The image display area DA is, for example, shaped in a rectangle and iscomposed of a plurality of pixels PX arrayed in an m×n matrix where eachof m and n is a positive integer. The display device DSP-1 comprises aplurality of signal wirings (not shown) in the image display area DA.The signal wirings include a plurality of scanning lines (not shown), aplurality of power supply lines (not shown) disposed parallel to thescanning lines, and a plurality of data signal lines (not shown)arranged orthogonally to the scanning lines.

The display device DSP-1 comprises the flexible substrate SUB as shownin FIG. 2 and FIG. 3. The flexible substrate SUB is a bendable,electrically insulating board and is formed of a flexible materialcontaining, e.g., polyimide (PI) as a major component. The flexiblesubstrate SUB has a thickness ranging, for example, 5 to 30 μm. Notethat materials having a high heat resistance such as polyamidimide andpolyaramide may be used instead of polyimide as the material of theflexible substrate SUB. It should be noted that the flexible substrateSUB is exposed to a high-temperature process during formation of a firstinsulating film 11, a second insulating film 12, a third insulating film13, switching elements SW and the like. For this reason, the flexiblesubstrate SUB has a high heat resistance. The flexible substrate SUB ofthe display device DSP-1 of the first embodiment does not need to havetransparency but the flexible substrate SUB may be colored. The flexiblesubstrate SUB can be formed by, for example, coating a temporary boardsuch as a glass board with a material such as polyimide. The temporaryboard used in forming the flexible substrate SUB is peeled off from theflexible substrate SUB after drive circuits and external circuits aremounted on the display device DSP-1.

The first insulating film 11 is disposed on the flexible substrate SUB.The first insulating film 11 suppresses ionic impurities, moisture andthe like entering from the flexible substrate SUB into the switchingelement which will be explained later. The first insulating film 11 isformed of, for example, an inorganic material such as silicon nitride(SiN), silicon oxide (SiO) or silicon oxynitride (SiON) and isconstituted as a single-layer body or a stacked layer body.

Switching elements SW1, SW2 and SW3 are disposed on the first insulatingfilm 11, in the image display area DA. The switching elements SW1, SW2and SW3 correspond to one pixel PX, respectively. For example, theswitching element SW1 corresponds to a red pixel, the switching elementSW2 corresponds to a green pixel and the switch in element SW3corresponds to a blue pixel. Each of the switching elements SW1, SW2 andSW3 is, for example, a thin-film transistor (TFT) including asemiconductor layer SC. Since the switching elements SW1, SW2 and SW3have the same structures, the structure of the switching element SW1will be specifically explained here.

The switching element SW1 is constituted as a top-gate type switchingelement but may be a bottom-gate type switching element. The switchingelement SW1 comprises a semiconductor layer SC formed of, for example,amorphous silicon. The semiconductor layer SC includes a channel region,a source region, and a drain region. The semiconductor layer SC iscovered with the second insulating film 12. The second insulating film12 is disposed also on the first insulating film 11. The secondinsulating film 12 is formed of an inorganic material, e.g.,tetraethylorthosilicate (TEOS).

A gate electrode WG of the switching element SW1 is disposed on thesecond insulating film 12 and located just above the channel region ofthe semiconductor layer SC. The gate electrode WG is covered with thethird insulating film 13. The third insulating film 13 is disposed alsoon the second insulating film 12. The third insulating film 13 is formedof an inorganic material, e.g., tetraethylorthosilicate (TEOS). A sourceelectrode WS and a drain electrode PD of the switching element SW1 arelocated on the third insulating film 13 and are in contact with thesource region and the drain region of the semiconductor layer SC throughcontact holes formed in the third insulating film 13.

A signal wiring SGL is located on the third insulating film 13 and iselectrically connected with the switching element SW1. The signal wiringSGL extends to the contact area CA adjacent to the image display areaDA. The signal wiring SGL is formed of, for example, MoW or the like.

The source electrode WS, the drain electrode WD and the signal wiringSGL are covered with the first organic film 14. The first organic film14 is disposed also on the third insulating film 13. The first organicfilm 14 is formed of an organic material having a high buffering, orshock-absorbing property such as a hard resin coat (HRC). A reflectivelayer 15 is disposed on the first organic film 14. The reflective layer15 is formed of, for example, aluminum or silver.

First electrodes PE are disposed on the reflective layer 15 and areelectrically connected to the drain electrodes WD of the respectiveswitching elements SW1, SW2, and SW3 through the contact holes formed inthe first organic film 14. The first electrodes PE are formed of, forexample, a transparent conductive material such as indium tin oxide(ITO) or indium zinc oxide (IZO).

A rib 16 is disposed in, for example, a grating shape or a stripe shapeto electrically insulate the first electrodes PE on the first organicfilm 14 on which the image display area DA is located, from each other.

A first connection wiring LL1 is located on the first organic film 14and is electrically connected with the signal wiring SGL on the thirdinsulating film 13 through a first contact hole CH1 formed in the firstorganic film 14, in the terminal area TA, as shown in FIG. 2. The firstconnection wiring LL1 is formed of, for example, MoW/Al or the like.

A second connection wiring LL2 is located on the first organic film 14and is electrically connected with the signal wiring SGL on the thirdinsulating film 13 through a second contact hole CH2 formed in the firstorganic film 14, in the terminal area TA, as shown in FIG. 3. The secondconnection wiring LL2 is formed of, for example, MoW/Al or the like.

The first connection wiring LL1 and the second connection wiring LL2 arecovered with a second organic film 17. The second organic film 17 isdisposed also on the first insulating film 14. The second organic film17 is formed of an organic material having a high buffering, orshock-absorbing property such as a hard resin coat (HRC), photosensitivetransparent acrylic resin or photosensitive transparent polyimide. Thesecond organic film 17 is formed of the same material as the rib 16 andcan be formed in the same process as the rib 16.

A first pad electrode PD1 is located on the second organic film 17 inthe pad area PA as shown in FIG. 2, and is electrically connected withthe first connection wiring LL1 through a third contact hole CH3 formedin the second organic film 17.

A second pad electrode PD2 is located on the second organic film 17 inthe pad area PA as shown in FIG. 3, and is electrically connected withthe second connection wiring 112 through a fourth contact hole CH4formed in the second organic film 17.

The first pad electrode PD1 and the second pad electrode PD2 areelectrically connected with drive circuits and external circuits (notshown) and can receive a power supply voltage and various signals fromthe drive circuits and external circuits.

The first contact holes CH1 and the second contact holes CH2 arealternately arranged in the first direction X as shown in FIG. 4. Inother words, the first contact holes CH1 and the second contact holesCH2 are arranged in a zigzag state in planar view. The third contactholes CH3 and the fourth contact holes CH4 are alternately arranged inthe first direction X, i.e., arranged in a zigzag state, as shown inFIG. 4. If the first contact holes CH1 and the second contact holes CH2or the third contact holes CH3 and the fourth contact holes CH4 arearranged linearly, increase in arrangement density of the connectionwiring and the pad electrodes is limited due to the surface areaassigned to the first contact holes CH1 and the second contact holesCH2, the third contact holes CH3 and the fourth contact holes CH4 or thelike. However, the first connection wirings LL1, the second connectionwirings LL2, the first to forth contact holes CH1, CH2, CH3 and CH4, andthe pad electrodes PD can be disposed at higher density, since the firstcontact holes CH1 and the second contact holes CH2 are arranged to bedisplaced from each other in the first direction X and the third contactholes CH3 and the fourth contact holes CH4 are arranged to be displacedfrom each other in the first direction X by arranging the first contactholes CH1 and the second contact holes CH2 and/or the third contactholes CH3 and the fourth contact holes CH4 in a zigzag state.

In the display device DSP-1, in the pre-bent state as shown in FIG. 5A,the contact area CA, the bend area BA and the pad area PA are arrangedto be adjacent to each other in the second direction Y, in the terminalarea TA. In the bent state as shown in FIG. 5B, the bend area BA is bentsuch that the pad area PA is located under the image display area DA ofthe flexible substrate SUB.

The display device DSP-1 of the first embodiment is an active-matrixdisplay device and, an organic light-emitting layer, a second electrode,a sealing layer, a counter substrate, and the like are disposed on thefirst electrode PE though not illustrated.

According to the first embodiment, the width of the terminal area TA canbe made smaller and the image display area DA can be effectivelyenlarged by bending the bend area BA such that the pad area PA islocated under the image display area DA of the flexible substrate SUB,in the terminal area TA, as shown in FIG. 5B.

In addition, if the bend area BA in the state shown in FIG. 5A is bentas shown in FIG. 5B, a bending stress is applied to the first to thirdinsulating films 11 to 13 located in the bend area BA and crack mayoccur. For this reason, crack may be propagated to the first connectionwirings LL1 and the second connection wirings LL2 located above thefirst to third insulating films 11 to 13 located in the bend area BA.

In the display device DSP-1 of the first embodiment, however, the firstconnection wirings LL1 and the second connection wirings LL2 are not indirect contact with the first to third insulating films 11 to 13 but areprovided on the first organic film 14. Furthermore, the first connectionwirings LL1 and the second connection wirings LL2 are covered with thesecond organic film 17. In other words, the first connection wirings LL1and the second connection wirings LL2 are located between the firstorganic film 14 and the second organic film 17. As a result, even ifcrack occurs in the first to third insulating films 11 to 13 located inthe bend area BA of the display device DSP-1, propagation of the crackcan be suppressed by the first organic film 14. In addition, since thefirst connection wiring LL1 and the second connection wiring LL2 arelocated between the first organic film 14 and the second organic film17, a break in the first connection wiring LL1 and the second connectionwiring LL2 can be suppressed. Therefore, a break in the first connectionwiring LL1 and the second connection wiring LL2 can be suppressed andthe high-reliability display device DSP-1 can be obtained.

Second Embodiment

A display device DSP-2 of the second embodiment will be described withreference to FIG. 6 and FIG. 7. FIG. 6 is a schematic cross-sectionalview of the display device DSP-2, corresponding to the cross-sectionalview of the DSP-1 shown in FIG. 2. FIG. 7 is a schematic cross-sectionalview of the display device DSP-2, corresponding to the cross-sectionalview of the DSP-1 shown in FIG. 3. Note that the plan view of thedisplay device DSP-2 is the same as the plan view of the display deviceDSP-1 shown in FIG. 1. The same members as those of the first embodimentexplained with reference to FIG. 1 to FIG. 5B are denoted by the samereference numerals and their detailed descriptions are omitted.

In the display device DSP-2 of the second embodiment, the firstinsulating film 11, the second insulating film 12 and the thirdinsulating film 13 are disposed in the contact area CA and the pad areaPA but are not disposed in the bend area BA, in the terminal area TA. Inother words, the first to third insulating films 11 to 13 do not existon the flexible substrate SUB located in the bend area BA.

The signal wiring SGL is located on the third insulating film 13 and iselectrically connected with the switching element SW1. The signal wiringSGL extends to the contact area CA adjacent to the image display areaDA. The signal wiring SGL is formed of, for example, MoW or the like.The source electrode WS, the drain electrode WD and the signal wiringSGL are covered with a first organic film 21. The first organic film 21is disposed also on the third insulating film 13. The first organic film21 is disposed also on the flexible substrate SUB. The first organicfilm 21 is formed of an organic material having a high buffering, orshock-absorbing property such as a hard resin coat (HRC).

The first connection wiring LL1 is disposed on the first organic film 21and is electrically connected with the signal wiring SGL on the thirdinsulating film 13 through a first contact hole CH1 formed in the firstorganic film 21, in the terminal area TA, as shown in FIG. 6. The secondconnection wiring LL2 is disposed on the first organic film 21 and iselectrically connected with the signal wiring SGL on the thirdinsulating film 13 through a second contact hole CH2 formed in the firstorganic film 21, in the terminal area TA, as shown in FIG. 7.

The first connection wiring LL1 and the second connection wiring LL2 arecovered with the second organic film 17. The second organic film 17 isdisposed also on the first insulating film 21. The second organic film17 is formed of an organic material having a high buffering, orshock-absorbing property such as a hard resin coat (HRC), photosensitivetransparent acrylic resin or photosensitive transparent polyimide.

In the display device DSP-2, in the pre-bent state similar to the stateexplained with reference to FIG. 5A, the contact area CA, the bend areaBA and the pad area PA are arranged to be adjacent to each other in thesecond direction Y, in the terminal area TA. In the display device DSP-2of the second embodiment, the bend area BA is bent such that the padarea PA is located under the image display area DA of the flexiblesubstrate SUB, similarly to the state shown in FIG. 5B.

According to the second embodiment, the width of the terminal area TAcan be made smaller and the image display area DA can be effectivelyenlarged by bending the bend area BA such that the pad area PA islocated under the image display area DA of the flexible substrate SUB,in the terminal area TA, as shown in FIG. 5B.

In addition, according to the second embodiment, the first to thirdinsulating films 11 to 13 do not exist in the bend area BA as shown inFIG. 6 and FIG. 7. In other words, according to the second embodiment,the first organic film 21, the first connection wiring LL1, the secondconnection wiring LL2, and the second organic film 17 are disposed inthe bend area BA. As a result, even if a bending stress is applied tothe bend area BA, a break in the first connection wiring LL1 and thesecond connection wiring LL2 can be suppressed since the first to thirdinsulating films 11 to 13 in which crack easily occurs do not exist. Inaddition, since the first connection wiring LL1 and the secondconnection wiring LL2 are located between the first organic film 21 andthe second organic film 17, a break in the first connection wiring LL1and the second connection wiring LL2 can be further suppressed. Thehigh-reliability display device DSP-2 can be therefore obtained.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the inventions.

What is claimed is:
 1. An electronic device comprising: a flexiblesubstrate; a first inorganic film provided on the flexible substrate; aswitching element provided on the first inorganic film; a wiringelectrically connected with the switching element; and a pad electrodeelectrically connected with the wiring, wherein the flexible substrateincludes a first portion, a second portion, and a third portion, thesecond portion is between the first portion and the third portion, thefirst inorganic film is not provided in the second portion, the secondportion is able to be bent, and in the second portion, a first organicfilm is between the flexible substrate and the wiring, and is directlyin contact with a surface portion of the flexible substrate.
 2. Theelectronic device according to claim 1, wherein a thickness of the firstorganic film in the portion is different from a thickness of the firstorganic film other than the portion.
 3. The electronic device accordingto claim 1, wherein the pad electrode is located in the third portion.4. The electronic device according to claim 1, further comprising: asecond inorganic film provided on a semiconductor layer of the switchingelement; and a third inorganic film provided on a gate electrode of theswitching element, wherein, in the second portion, the second inorganicfilm, and the third inorganic film are not provided.
 5. The electronicdevice according to claim 4, wherein, in the first portion and the thirdportion, the first inorganic film, the second inorganic film, and thefirst organic film are between the flexible substrate and the wiring. 6.The electronic device according to claim 5, wherein a thickness of thefirst organic film in the second portion is larger than a thickness ofthe first organic film in the first portion and the third portion. 7.The electronic device of claim 1, further comprising a second organicfilm covering the wiring, wherein the wiring is between the firstorganic film and the second organic film.
 8. The electronic deviceaccording to claim 1, wherein the flexible substrate is formed ofpolyimide.
 9. The electronic device according to claim 1, wherein thewiring includes a signal wiring and a connection wiring, and theconnection wiring is provided on the first organic film.
 10. Theelectronic device according to claim 9, wherein the signal wiring andthe connection wiring are connected to each other through a firstcontact portion provided in the first organic film.
 11. The electronicdevice according to claim 5, wherein the wiring includes a signal wiringand a connection wiring, and the signal wiring is provided on the thirdinorganic film.
 12. The electronic device according to claim 11, whereinthe signal wiring and the connection wiring are connected to each otherthrough a first contact portion provided in the first organic film. 13.The electronic device according to claim 12, wherein the first contactportion is located in the first portion.